I believe you have to click one of the snapshots in the menu (those that you have taken before). This will change the troop values on the map back to what they were when the snapshot was taken. Then click Analyze Snapshot, and the numbers that have changed will have blinking boxes put around them, of the colour matching their current live owners.

One never knows just where a question is coming from. Since you didn't post in the Tools Suggestions & Bugs forum, I thought you just weren't sure what to expect. So, presuming that you have not run into the situation where the troop numbers are completely unchanged since the snapshot was taken, leaving nothing to highlight, we need to know a little more about the situation. Post the browser you are using and its version, the version of Greasemonkey if you use it, and the names and versions of any other scripts/addons you have, then we can shift this into the Tools Suggestions & Bugs forum and get some feedback.